System for fixing a furniture leg to a furniture and method for fixing the furniture leg to the furniture

ABSTRACT

A system (3) for fixing a furniture leg to a furniture comprises a fixing element (4) and a retaining element (5). The retaining element (5) comprises a first and a second protrusion on one side. The fixing element (4) comprises a first side (S1), a second side (S2) adjoining the first side (S1), and a third side (S3) opposite to the first side (S1), a recess (6) being open towards the first side (S1) and a pretension face (7) starting from the second side (S2) and running along the third side (S3) and a stop face (8) adjoining the pretension face (7) and protruding from the third side (S3). The retaining element (5) and the fixing element (4) are configured such that the system (3) enables fixation without backlash of the furniture leg to the furniture in a state in which the first protrusion is in contact with the recess (6) and the second protrusion is in contact with the pretension face (7) without backlash.

The invention relates to a system for fixing a furniture leg to a furniture and a method for fixing the furniture leg to the furniture, in particular, a system for fixing a furniture leg to a furniture and a method for fixing the furniture leg to the furniture, which system and method enable a simple assembly.

Usually, pieces of furniture comprise several components. For example, a table consists of a frame element to which, on one side, a tabletop and, on the other side, table legs or furniture legs are fixed.

If a customer buys such a piece of furniture, the piece of furniture has to be shipped by the manufacturer, the wholesaler, or the retailer to the customer. For a space-saving transport, the furniture is shipped in a state being disassembled into its components. At the end customer, for example, the individual furniture legs has to be mounted to the piece of furniture.

From the state of the art, designs by which a furniture leg can be attached to a piece of furniture without the aid of tool, for example, by means of a locking device are known. However, such designs according to the state of the art have the disadvantage that the furniture legs attached to a furniture in such a manner are not attached without backlash. Therefrom, a susceptibility for vibrations of the furniture results.

However, according to the “Anforderungen und Prüfungen von Büromöbeln—Leitfaden für die Sicherheitsanforderungen an Büro-Arbeitstische und Büroschränke in Deutschland” (siehe DIN Fachbericht 147, Juni 2006, Punkt 3.6) of the DIN Institute (German Institute for Standardization, registered society), it must be ensured by the design of a bureau working desk that vibrations are prevented. Hereto, a specific test by means of a pendulum hammer is foreseen. Designs according to the state of the art envisaging fixation of a furniture leg to a furniture without the aid of a tool do usually not fulfill the criteria of the DIN Institute in regard of the absence of vibration.

From the state of the art document DE 10 2005 037 394 A1, such a pedestal fixation system in which a locking mechanism for a tool-less locking of a table leg on a table is disclosed is known. In the disclosed design, the table leg is obliquely inserted into a recess of the table and locking is initiated by a locking element by means of tilting (or erecting) the table leg. By this design, usually, no backlash free fixation of the table leg within the recess will be achieved unless the dimensions of the parts to be interlocked, i.e., the recess and the headpiece, would be designed as a press-fit which would be elaborate and extremely expensive in the production. Moreover, the assembly would only be possible with extremely high effort since, for a press-fit, the parts have to be pressed in with high force in order to be held securely.

It is therefore the object of the present invention to provide a system for fixing a furniture leg to a furniture by which a furniture leg can be fixed to a furniture quickly, simply, economically and without backlash, and, moreover, without the aid of a tool.

The object is achieved by a system according to claim 1 and a method according to claim 12. Advantageous further developments of the invention are included in the dependent claims.

According to an aspect of the invention, a system for fixing a furniture leg to a furniture comprises a fixing element which is configured to be fixable to a furniture leg and a retaining element which is configured to be fixable to the furniture. On one side, the retaining element comprises a first protrusion and a second protrusion spaced from the first protrusion. The fixing element has a first side, a second side adjacent to the first side and a third side opposite the first side. Further, the fixing element has a recess being open towards the first side, which recess being configured to accommodate the first protrusion, a pretension face starting from the second side running along the third side, and a stop face protruding from the third side and adjoining the pretension face.

The retaining element with the first protrusion and the second protrusion, and the fixing element with the recess, the pretension face, and the stop face are configured such that, in a state in which the first protrusion is in contact with the recess from the first side at a predetermined depth and, at the same time, without backlash on both sides and the second protrusion is in contact with the pretension face and the stop face without backlash, the system enables a backlash free fixation of the furniture leg to the furniture.

By such a configuration of the system, it is possible to mount the furniture leg simply and without backlash on the furniture by means of simple and economic means.

In an advantageous further development of the system, the first protrusion is formed by a first axle and the second protrusion is formed by a second axle respectively protruding from the retaining element.

Axles can be purchased or manufactured and stored simply and economically so that an economic production is supported.

According to a further advantageous further development of the system, the first axle and the second axle are arranged between the opposite sides of the retaining element in a protruding manner and the fixing element comprises two recesses respectively configured to accommodate the first axle and two pretension faces and two stop faces with which the second axle is respectively in contact.

By the provision of the first and second axles on opposite sides, wherein the sides can be averted or face each other, a stability of the system is increased and a position of the furniture leg with respect to the furniture can easily be determined.

In a further advantageous further development of the system, the retaining element comprises orifices for accommodating the axles, and at least one of the orifices has a cross-section which is configured to enable a force-free insertion of one of the first and second axles into the at least one orifice, and that, in the state in which the first axle is in contact with the recess from the first side at the predetermined depth and, at the same time, without backlash on both sides and the second axle is in contact with the pretension face and the stop face without backlash, at least one of the first and second axles and at least one of the orifices have two contact points.

By the cross-section enabling the force-free insertion, therefore, for example, a free cross-section larger than a diameter of the axle, the axle can be mounted simply and quickly to the retaining element. Therefore, in the position in which the first protrusion is in contact with the recess from the first side at the predetermined depth and, at the same time, without backlash on both sides, and the second protrusion is in contact with the pretension face and the stop face without backlash, an absolutely backlash free and statically determined fixation is possible by the two contact points in the mounted position.

In an advantageous further development of the system, at least one orifice comprises an oval cross-section.

An oval cross-section for enabling or providing the two contact points can be manufactured in an easy and economic manner.

In a next advantageous further development of the system, the fixation element is configured such that a distance between a central axis of the first axle and the pretension face is not constant along the course of the pretension face from the second side toward the stop face, wherein the first axle is in contact with the recess at the predetermined depth and, at the same time, without backlash on both sides.

By the non-constant distance, it is enabled that zero backlash of the system is easily to be achieved in the position where the second axle is in contact with the stop face and, without backlash, with the pretension face or that in this position, a pretension force between the protrusions, the recess and the pretension force is generated easily in a requested manner by accordingly attuning the distance in advance.

In a next advantageous further developments of the system, the pretension face comprises a first area along which the distance increases starting from the second side and a second area adjoining the first area, along which, starting from the second area, the distance decreases or maintains constant.

By the provision of these two areas, the behavior of the fixing element with respect to the retaining element can be influenced during the assembly. Since the distance increases in the first area, either zero backlash is gradually generated or the pretension force is exerted in a controlled manner when the axle moves along the pretension face. In the second area, the zero backlash or the pretension force can easily be maintained since no force component acts such that the connection is released.

Moreover, a transition from the first to the second area can be detected by an assembly operator in a tactile manner so that reaching of the final position can be detected in a perceptible manner by the assembly operator.

In a further advantageous further development of the system, the recess comprises a dimension in direction towards the second side which, starting from the first side, decreases towards the third side.

Such a shape of the recess can be easily manufactured and, thereby, the position of the first axle in which it is in contact with the recess from the first side at the predetermined depth and, at the same time, without backlash on both sides, can easily be determined by attuning with the diameter of the axle.

According to another advantageous further development of the system, the system comprises a locking device. The locking device fixes the fixing element with respect to the retaining element in the state in which the first protrusion is in contact with the recess from the first side at a predetermined depth and, at the same time, on both sides and the second protrusion is in contact with the stop face and, without backlash, with the pretension face.

By this locking device, the position in which the second protrusion is in contact with the stop face can be secured so that the backlash free connection between the retaining element and the fixing element is not released, also, for example, when lifting the table at the tabletop.

In a further advantageous further development of the system, the locking device is attached to the retaining element and comprises a bar movable relatively to the retaining element and a pretension element configured such that the bar is urged in a locking direction into a locking position in which the locking device locks the position of the second protrusion in contact with the stop face.

In an advantageous further development of such a system, the locking device is arranged on the retaining element and configured such that the locking direction runs parallel to a direction of protruding of the first and second protrusion.

By this arrangement, it is possible to subsequently release again the locking in an ergonomic manner.

According to another aspect of the invention, a method for fixing a furniture leg to a furniture comprises the following steps: inserting the first protrusion of the retaining element into the recess of the fixing element being open towards the first side; performing a slewing between the fixing element and the retaining element such that the second protrusion of the retaining element moves along the pretension face so that the first protrusion is in contact with the recess at the predetermined depth and without backlash on both sides and the second protrusion is in contact with the stop face and, without backlash, with the pretension face.

By this method, it is possible to mount the furniture leg simply and without backlash by simple and economic means.

According to an advantageous further development of the method, the position in which the second protrusion is in contact with the stop face is locked.

Thereby, the position in which the second protrusion is in contact with the stop face can be secured so that the connection between the retaining element and the fixing element is not released, for example, also when lifting the table by the tabletop.

In an advantageous further development of the method, the second protrusion is firstly moved in a first area of the pretension face in which a distance between a central axis of a first axle being in contact with the recess at the predetermined depth and, at the same time, without backlash on both sides, and being the first protrusion and the pretension face along the course of the pretension face from the second side towards the stop face increases. Thereby, a pretension force between the protrusions, the recess and the pretension face is exerted or a zero backlash is generated. Then, the second protrusion moves in a second area of the pretension face in which the distance decreases or remains constant in order to automatically maintain the position of the second protrusion in contact with the stop face.

By these features of the method, the behavior of the fixing element with respect to the retaining element during the assembly can be influenced. Since the distance increases in the first area, either the pretension force is exerted in a controlled manner or a zero backlash is gradually generated when moving the axle along the pretension face. In the second area, the zero backlash or the pretension force can easily be maintained since no first component acts such that the connection is released.

In a further advantageous further development of the method, a transition between the first and the second area of the pretension face can be detected in a tactile manner.

By the transition, the reaching of a final assembly position, namely, the position in which the second protrusion is in contact with the stop face and the connection without backlash is established can be reported to an assembly operator by a perceptible or audible engagement.

Below, the invention is elucidated with reference to the attached drawings.

In particular,

FIG. 1 shows a lateral cross-sectional illustration of a table with a table leg mounted thereto;

FIG. 2 shows a lateral cross-sectional illustration of the table of FIG. 1 with the table leg in a state before it is completely mounted;

FIG. 3 shows an enlarged detail view of a detail A in FIG. 1;

FIG. 4 shows an enlarged detail view of a detail B in FIG. 1; and

FIG. 5 shows a sectional view from the front of the table of FIG. 1 having a locking device.

FIG. 1 shows a lateral cross-sectional illustration of a table 1 being an embodiment of a furniture having a table leg 2 mounted thereto being an embodiment of a furniture leg. The table 1 comprises a system 3 which, in turn, comprises a fixing element 4 and a retaining element 5 in order to fix the table leg 2 to the table 1.

The fixing element 4 is fixed to the table leg 2 and comprises a first side S1, a second side S2 adjacent to the first side S1 and a side S3 opposite the first side S1.

Further, the fixing element 4 comprises a recess 6 being open towards the first side S1. Starting from the second side S2, a pretension face 7 is provided running along the third side S3. Further, a stop face 8 adjoining the pretension face 7 and protruding from the third side S3 is provided on the fixing element 4. In this embodiment, a lower end of the pretension face 7 and the stop face 8 are provided in an indention or a recess of the fixing element 4. In an alternative embodiment, the invention is not provided. A provision of the pretension face 7 and the stop face 8 on an open third side S3 is also possible.

The retaining element 5 is fixed to the table 1. On one side, the retaining element 5 comprises a first axle 9 and a second axle 10 spaced from the first axle 9, the first axle 9 and the second axle 10 protruding from the retaining element 5 from the side. The first axle 9 and the second axle 10 are arranged in parallel. In an alternative embodiment, no axles are provided but, instead, a first suitable protrusion and a second suitable protrusion spaced therefrom are provided. In a further alternative embodiment, the axles 9, 10 are not arranged in parallel but they are arranged in another suitable posture with respect to one another in which a pretension or zero backlash can be exerted on the system.

The recess 6 of the fixing element 4 is configured to accommodate the first axle 9. The recess 6 comprises a dimension in direction of the second side S2 which decreases coming from the first side S1 towards the third side S3. Alternatively, the greater a depth in the recess 6 is, it is not mandatorily necessary that the dimension decreases in the direction of the second side S2. A constant dimension in direction of the second side S2 is also possible if the dimension is attuned to a diameter of the first axle 9 such that an accommodation without backlash is ensured.

In FIG. 1, a state is shown in which the first axle 9 is in contact with the recess 6 from the first side S1 at a predetermined depth and, at the same time, without backlash on both sides and the second axle 10 is in contact with the stop face 8 and, without backlash, with the pretension face 7. In this state, the retaining elements with the first protrusion and the second protrusion and the fixing element with the recess, the pretension face and the stop face are configured such that a fixation of the table leg 2 to the table 1 without backlash is enabled.

FIG. 2 shows a lateral cross-sectional illustration of the table 1 of FIG. 1 with the table leg 2 in a state before it is completely mounted.

The first axle 9 is already inserted from the first side S1 into the predetermined depth and, thereby, it is in contact with the recess 6 on both sides without backlash. The second axle 10 is illustrated in a state in which it moves along the pretension face 7 in order to generate a pretension between the first axle 9 and the recess 6. Alternatively, zero backlash therebetween can be maintained or generated.

FIG. 3 shows an enlarged detail view of detail A in FIG. 1. The retaining element 5 comprises an orifice 11 for accommodating the first axle 9. The orifice 11 comprises a cross-section which is configured to enable a force-free insert of the first axle 9. Thereto, the orifices 11 comprises a free cross-section which is larger than a diameter of the first axle 9.

In the state shown in FIG. 1 in which the first axle 9 is in contact with the recess 6 from the first side S1 at the predetermined depth and without backlash on both sides and the second axle 10 is in contact with the pretension face 7 and, without backlash, with the stop face 8, the first axle 9 and the orifice 11 have two contact points K1, K2. The orifice 11 has an oval cross-section which is configured to enable the free cross-section and the both contact points K1, K2. In an alternative embodiment, the orifice 11 does not have an oval shape but another suitable shape, for example, an ellipse.

Simultaneously, the first axle 9 and the recess 6 have to contact points K3, K4. Thereby, the connection without backlash between the fixing element 4 and the retaining element 5 at the first axle 9 is ensured.

FIG. 4 shows an enlarged detail view of a detail B in FIG. 1. The retaining element 4 comprises an orifice 12 for accommodating the second axle 10. The orifice 12 has a cross-section configured to enable a force-free insert of the second axle 10. Thereto, the orifice 12 has a free cross-section which is larger than a diameter of the second axle 10.

In the state shown in FIG. 1 in which the first axle is in contact with the recess from the first side S1 at the predetermined depth and, at the same time, without backlash on both sides and the second axle 10 is in contact with the pretension face 7 and the stop face 8 without backlash, the second axle 10 and the orifice 12 have two contact points K5, K6. The orifice 12 has an oval cross-section in order to enable the free cross-section and the both contact points K5, K6. In an alternative embodiment, the orifice 12 does not have an oval shape but another suitable shape, for example, an ellipse.

In FIG. 1, a distance D between a central axis MA of the first axle 9 at the predetermined depth and, at the same time, in contact with the recess 6 on both sides without backlash and the pretension face 7 is shown. In FIG. 4 is shown that the distance D is not constant along the course of the pretension face 7 from the second side S2 to the stop face 8.

In particular, the pretension face 7 comprises a first area 7 a along which, coming from the second side, the distance D increases in order to pretension the system or, alternatively, eliminate a backlash from the system by the motion of the second axle 10 along the pretension face 7. Further, the pretension face 7 comprises a second area 7 b along which the distance D, starting from the first area 7 a, decreases. In an alternative embodiment, the distance D in the second area 7 b remains constant.

In an alternative embodiment, the distance between the central axle MA of the first axle 9 at the predetermined depth and, at the same time, in contact with the recess 6 on both sides without backlash and the pretension face 7 can be constant, wherein, then, zero backlash can be ensured without pretensioning or further pretensioning the system by the motion of the second axle 10 along the pretension face 7.

FIG. 5 is a sectional view from the front of the table of FIG. 1 with a locking device 13.

In FIG. 5 is illustrated that the second axle 10 is arranged in a protruding manner between opposite sides of the retaining element 5. Although not illustrated, the first axle 9 is also arranged in a protruding manner between the opposite sides of the retaining element 5.

The fixing element 5 comprises two recesses 6 respectively accommodating the first axle 9 and two pretension faces 7 and two stop faces 8 with which then the second axle 10 respectively is in contact.

In an alternative embodiment, the first and second axles 9, 10 merely protrude outside from one side of the retaining element 5 or from both sides from the retaining element 5, wherein, then, as the case may be, only one recess 8 and, respectively, only one pretension face 7 and stop face 8 are provided.

The locking device 13 is attached to the retaining element 5 and comprises a bar 14 movable relatively to the fixing element 5. Further, the locking device 13 comprises a pretension element 15 urging the bar 14 in an locking direction VR into a locking position in which the locking device 13 locks the position of the second axle 10 in contact with the stop face 8.

Thereby, the fixing element 4 is fixed to the retaining element 5 in the state in which the first axle 9 is in contact with the recess 6 from the first side S1 at the predetermined depth and, at the same time, on both sides and the second axle 10 is in contact with the stop face 8 and, without backlash, with the pretension face 7.

The locking device 13 is arranged on the retaining element 5 such that the locking direction VR runs parallel to a direction of the protruding of the first and second axles 9, 10.

In alternative embodiments, it is possible that the locking device 13 is not provided with a pretension element but, instead, it can be locked manually, furthermore, it can be attached not to the retaining element but to the fixing element and, except from that, it can comprise another locking device. It is essential that the system is fixed in the state in which the first axle 9 is in contact with the recess 6 from the first side S1 at the predetermined depth and, at the same time, without backlash on both sides and the second axle 10 is in contact with the stop face 8 and, without backlash, with the pretension face 7.

In use, for fixing the table leg 2, firstly the first axle 9 of the retaining element 5 is inserted into the recess 6 of the fixing element 4 being open towards the first side S1. Thereby, the retaining element 5 is moved thus far that the first axle 9 is in contact with the recess 6 on both sides. Thereby, it is ensured that the second axle 10 is positioned such that it can move along the pretension face 7 of the retaining element 5 without collision with the second side S2 of the retaining element 5. On the other hand, if the first axle 9 has not been sufficiently inserted in the recess 6, the second axle 10 seats on the second side S2 and the retaining element 5 can be moved relatively to the fixing element 4 such that the second axle 10 reaches the pretension face 7.

Subsequently, a slewing between the fixing element 4 and the retaining element 5 is performed so that the second axle 10 of the retaining element 5 moves along the pretension face 7 of the fixing element 4 until the first axle 9 is at the predetermined depth in the recess 6, and, at the same time, in contact without backlash on both sides and the second axle is in contact with the stop face 8 and, without backlash, with the pretension face 7. Depending on the mounting posture of the table 1, the fixing element is swiveled with respect to the retaining element 5 or the retaining element 5 is swiveled with respect to the fixing element 4.

When performing the slewing between the fixing element 4 and the retaining element 5 into the position in which the second axle 10 is in contact with the stop face 8, if the locking device 13 having the pretension element 15 for an automatic locking is provided, the system 3 is locked in an automatic manner.

During the slewing, the second axle 10 firstly moves in the first area 7 a of the pretension face 7 in which a distance between the central axis MA of the first axle 9 at the predetermined depth and, at the same time, in contact with the recess 6 without backlash on both sides and the pretension face 7 increases along the course of the pretensions face 7 from the second side S2 to the stop face 8 in order to generate a pretension force between the axles 9, 10, the recess 6 and the pretension face 7. Subsequently, the second axle 10 then moves into the second area 7 b of the pretension face 7 in which the distance D decreases in order to maintain the position of the second axle 10 in contact with the stop face 8 in a positively driven manner. Thereby, as the case may be, a transition between the first and the second area is tactilely detected without generating a pretension force.

All the features in the description, the subsequent claims, and the drawings can solitarily or in an arbitrary combination be relevant for the invention. 

1. System for fixing a furniture leg to a furniture, comprising: a fixing element configured to be fixable to the furniture leg, and a retaining element configured to be fixable to the furniture, wherein the retaining element comprises a first protrusion and a second protrusion spaced from the first protrusion on one side, the fixing element comprises a first side (S1), a second side (S2) adjacent to the first side (S1), and a third side (S3) opposite to the first side (S1), a recess being open towards the first side (S1), which recess is configured to accommodate the first protrusion and, a pretension face starting from the second side (S2) running along the third side (S3) and a stop face protruding from the third side (S3) and adjoining the pretension face, wherein the retaining element with the first protrusion and the second protrusion and the fixing element with the recess, the pretension face and the stop face are configured such that in a state in which the first protrusion is in contact with the recess from the first side (S1) at a predetermined depth and, at the same time on both sides, and the second protrusion is in contact with the stop face and, without backlash, with the pretension face, the system enables a fixation without backlash of the furniture leg to the furniture.
 2. System according to claim 1, wherein the first protrusion is formed by a first axle and the second protrusion is formed by a second axle which respectively protrude from the retaining element.
 3. System according to claim 2, wherein the first axle and the second axle are arranged between opposite sides of the retaining element in a protruding manner, and the fixing element comprises two recesses respectively configured to accommodate the first axle, and two pretension faces and two stop faces with which the second axle respectively are in contact.
 4. System according to claim 2, wherein the retaining element comprises orifices for accommodating the axles, and at least one of the orifices has a cross-section configured such that a force-free insert of one of the first axle and the second axle into the at least one orifice is enabled and that, in the state in which the first axle is in contact with the recess from the first side (S1) at the predetermined depth and, at the same time, without backlash on both sides, and the second axle is in contact with the stop face and, without backlash, with the pretension face, at least one of the first axle and the second axle and the at least one of the orifices have two contact points.
 5. System according to claim 4, wherein at least one orifice has an oval cross-section.
 6. System according to claim 2, wherein the fixing element is configured such that a distance (D) between a central axis (MA) of the first axle being in contact with the recess at the predetermined depth and, at the same time, without backlash on both sides, and the pretension face along the course of the pretension face from the second side (S2) to the stop face is not constant.
 7. System according to claim 6, wherein the pretension face comprises a first area along which, starting from the second side (S2), the distance (D) increases and a second area adjoining the first area along which, starting from the first area, the distance (D) decreases or remains constant.
 8. System according to claim 1, wherein the recess has a dimension in direction towards the second side (S2), which dimension decreases starting from the first side (S1) towards the third side (S3).
 9. System according to claim 1, wherein the system comprises a locking device locking the fixing element to the retaining element in the state in which the first protrusion is in contact with the recess from the first side (S1) at a predetermined depth and, at the same time, on both sides and the second protrusion is in contact with the stop face and, without backlash, with the pretension face.
 10. System according to claim 9, wherein the locking device is attached to the retaining element, and comprises a bar movable relatively to the retaining element and a pretension element configured such that it urges the bar in a locking direction (VR) into a locking position in which the locking device locks the position of the second protrusion in contact with the stop face.
 11. System according to claim 10, wherein the locking device is arranged on the retaining element such and is configured such that the locking direction (VR) runs parallel to a direction of protruding of the first and second protrusions.
 12. Method for fixing a furniture leg to a furniture by means of a system according to claim 1, having the steps: inserting the first protrusion of the retaining element into the recess of the fixing element being open towards the first side (S1); preforming a slewing between the fixing element and the retaining element such that the second protrusion of the retaining element moves along the pretension face of the fixing element so that the first protrusion is in contact with the recess at the predetermined depth and, at the same time, without backlash on both sides, and the second protrusion is in contact with the stop face and, without backlash, with the pretension face.
 13. Method according to claim 12 having the additional step locking the position in which the second protrusion is in contact with the stop face.
 14. Method according to claim 12, wherein the second protrusion moves firstly in a first area of the pretension face in which a distance (D) between a central axis (MA) of a first axle being in contact with the recess at the predetermined depth and, at the same time, without backlash on both sides, and being the first protrusion and the pretension face increases along the course of the pretension face from the second side (S2) to the stop face in order to exert a pretension force between the protrusions, the recess and the pretension face or to generate zero backlash, and the second protrusion then moves in a second area of the pretension face in which the distance (D) decreases or remains constant in order to automatically maintain the position of the second protrusion in contact with the stop face.
 15. Method according to claim 14, wherein a transition between the first area and the second area of the pretension face can be tactilely detected. 